1. Field of the Invention
The present invention relates to a substrate processing apparatus for transporting a substrate, such as a semiconductor substrate, a glass substrate for a liquid crystal display device, a glass substrate for a photomask, a substrate for an optical disk and the like, with a resist film formed thereon by coating the substrate with a resist into an exposure apparatus, and for performing a development process on an exposed substrate received from the exposure apparatus.
2. Description of the Background Art
As is well known, semiconductor and liquid crystal display products and the like are fabricated by performing a series of processes including cleaning, resist coating, exposure, development, etching, interlayer insulation film formation, heat treatment, dicing and the like on the above-mentioned substrate. An apparatus which performs a resist coating process on a substrate to transfer the substrate to an exposure apparatus and which receives an exposed substrate from the exposure apparatus to perform a development process on the substrate, among the above-mentioned processes, is widely used as a so-called coater-and-developer.
The exposure apparatus (also known as a stepper) for performing an exposure process is typically provided in juxtaposition with the above-mentioned coater-and-developer, and prints a circuit pattern on a substrate formed with a resist film. With recent decrease in width of lines exposed to light, a lamp for use in printing of a pattern in such an exposure apparatus is shifting from a conventional ultraviolet light source toward a KrF excimer laser light source and also toward an ArF excimer laser light source. A chemically amplified resist is used when a pattern is printed using a KrF light source and an ArF light source. The chemically amplified resist is a photoresist of the type such that an acid formed by a photochemical reaction during the exposure process acts as a catalyst for resist reactions such as crosslinking, polymerization and the like in the subsequent heat treatment step to change the solubility of the resist in a developing solution, whereby pattern printing is completed.
When the chemically amplified resist is used, a slight variation in processing conditions exerts a large influence upon line width uniformity because an extremely small amount of acid catalyst is formed during the exposure process. In particular, it is known that the time interval between the instant of the end of the exposure process and the instant of the start of a post-exposure bake process exerts the greatest influence on the line width uniformity. Thus, a technique for controlling the time interval between the end of the exposure process and the start of the post-exposure bake process to be constant is proposed, for example, in Japanese Patent Application Laid-Open No. 7-142356 (1995). Such a technique can improve the line width uniformity when the chemically amplified resist is used.
Unfortunately, some variations in line width occur even if the time interval between the end of the exposure process and the start of the post-exposure bake process is made constant. It is contemplated that an important factor other than the time interval between the end of the exposure process and the start of the post-exposure bake process is the time interval between the instant at which the resist coating process is completed and the instant at which the exposure process is executed. However, no particular consideration has conventionally been given to controlling this time interval.
In particular, the replacement of a current exposure pattern for printing with another involves a reticle change in the exposure apparatus, which in turn requires about two minutes. Thus, a substrate subjected to the resist coating process and formed with a resist film must be in a standby condition during the reticle change before the exposure process. This standby time interval has been a significant factor that causes a variation between substrates in the time interval between the completion of the resist coating process and the exposure process.
Requirements for the reduction in line width in semiconductor devices are becoming increasingly stringent. It is, therefore, highly desirable to reduce any slight variations in line width to a minimum.